Dowel support for bent-up reinforcement bars and process for the production thereof

ABSTRACT

A studrail for shear reinforcement for reinforced concrete slabs is composed of a spacing rail (5) and a plurality of studs (6) which are arranged in parallel at a certain distance and provided with enlarged dish-like anchor heads (8) at both ends. The spacing rail (5), produced as a shaped sheet metal rail, grips one anchor head (8) of each stud with its two opposing folded flange edges (10).

The invention relates to a studrail for shear reinforcement inreinforced concrete slabs, consisting of a spacing rail and a pluralityof parallel spaced studs that are clamped at one end by the rail. Thestuds consist of a shaft with disc shaped heads formed at both ends.

Shear reinforcement consisting of studrails are used in reinforcedconcrete slabs or beams in the area of supports, especially in the areaof slab-column connections to resist the shear forces in the supportarea caused by the column reactions and as such serves as punching shearreinforcement.

The known studrail of the above-mentioned type (EP 0 495 334 B1)features studs with disc shaped heads only at one end and are welded tothe rail at the other end. The production of the studrail is thereforerather elaborate. The heat generated by the welded connection may leadto a warping of the spacing rail, which must be straightened afterwards.Through the welding process, changes of material properties might occurin the stud that can lead to a reduced load bearing capacity.

The aim of the invention is therefore to develop the above-mentionedtype of studrail such that the production is simplified and the weldingis eliminated.

This objective is achieved by the invention by using a profiled sheetmetal channel as the spacing rail, the base plate of which is in contactwith the top face of the head of the stud and the folded flanges of thechannel are enclosing the opposite edges of the head of the stud.

Herewith a simple tightly fitting connection between the studs and thespacing is achieved without any welding. Thus no heat-induced changes inthe material properties occur in the stud head. A subsequentstraightening of the studrail is not necessary because no warping willoccur since there is no heat generated by the connection. The studrailcan be readily produced in any length, can be easily stored and shipped,without the hazard that the spacing or alignment of the individual studsis changed.

The purely mechanical attachment of the stud and the spacing railenables the selection of different material properties of the rail andthe stud. This in particular facilitates the production of a stainlesssteel studrail. Since there is no possibility of corrosion of stainlesssteel, the required concrete cover beneath the spacing rail can bereduced in this case.

In their preferred form, the flanges of the channel enclose the edges ofthe stud head in a clamping manner. Alternatively, provisions could bemade that each stud head has a limited movement along the spacing railto allow the spacing of the studs to be adjusted after fabrication.

According to a preferred form, it is planned that on the base of thechannel cross-section a projecting stop for the stud heads is providedat equal distances along the length of the channel. These stops could belips punched out of the profile base and bent through an angle againstwhich a stud head is held during the assemblage. Herewith an exactpositioning of the studs is guaranteed.

The stops could also be projections that engage into a recess of a studhead. Those projections could be produced with a center-hole punch.

According to another advantageous form of the invention it is plannedthat openings are provided in the base plate of the channel. Thus anintense connection with the surrounding concrete is achieved.

In the base plate of the channel openings can be provided to supportchairs. If the chairs are attached to the rail in such openings the samechairs can be used for different rail width, which means asimplification of storage. The openings can be elongated so that thechairs can be moved in the direction of the rail to facilitate anadjustment of the rail after the chair is attached to the formwork.

According to an advantageous modified form of the invention it isenvisioned that the edges of the flanges of the spacing rail have edgestrips bent outward. This arrangement will have the effect that theconcrete in the area of the stud head and especially at the underside ofthe stud head, which is the face of the stem joined to the stud head, isconfined so that even with a relative small stud head diameter it ispossible that a highly stressed support of the stud head is achieved inthe concrete.

Further advantageous design types of the invented studrail are subjectof further sub-claims.

The invention also refers to a procedure for production of the abovementioned studrails.

This procedure is described by the following steps:

a) sheet metal strip is rolled from a sheet metal coil;

b) the edges of the metal strip are bent upwards;

c) one head of the studs is set into the shaped sheet metal strip;

d) sidewalls of the shaped strip are folded inwards to provide aclamping action on the stud heads.

In this way the studrail can be produced in a continuous extensivelyautomated assembly and cut to the desired length. Advantageous forms ofthe invented production process are subject to further sub-claims.

Design examples of the invention are described in more detail and shownin the following drawings.

Shown in:

FIG. 1 is a section of a studrail in elevation and the contours of thereinforced concrete slab in which the studrail is embedded are indicatedwith dash-dotted lines,

FIG. 2 is a view along the line II--II in FIG. 1,

FIG. 3 is a view corresponding to FIG. 2 showing a modified form ofproduction with smooth stud stems,

FIG. 4 a view along the line IV--IV in FIG. 1,

FIG. 5 Corresponds to FIG. 4 showing a modified form of production,

FIG. 6 is a view along the line VI--VI in FIG. 5,

FIG. 7 is a diagram similar to FIG. 4 showing another modified form ofproduction of a studrail with sheet metal lips bent at an angel as stopsfor the studs,

FIG. 8 is a view along line VIII--VIII in FIG. 7

FIG. 9 is a top view of a studrail with openings in the bottom of theprofile,

FIG. 10 is a top view similar to FIG. 9 with an opening in the bottom ofthe profile,

FIG. 11 is a cross section of a spacing rail in a modified form ofproduction before inserting the studs,

FIG. 12 is a vertical section through a reinforced concrete beam with astudrail,

FIG. 13 is a view a long the line XIII--XIII in FIG. 12,

FIG. 14 is a three dimensional diagram of another modified form ofproduction of the studrail, and

FIG. 15 is a schematic diagram of the production method for a studrail.

The studrail 1 shown in FIGS. 1, 2 and 4 is used to assemble shearreinforcement consisting of a plurality of studrails in a reinforcedconcrete slab 2 which has both a top 3 and bottom 4 layer ofreinforcement. The studrail 1 consists of several studs 6 attached to aspacing trough or rail 5. The studs 6 are positioned parallel to eachother and at a specified spacing. Each stud 6 has an elongate stud shaft7 which consists of deformed reinforcing steel as shown in various formsin FIG. 1, 2 and 4. On both ends of the stud shaft 7 a disc shapedwidened stud head 8 is provided.

One of the heads 8 of each stud 6 is attached to the spacing rail 5. Thespacing rail 5 consists of a profiled sheet metal strip, which touchesthe flat base 9 to the top face of the upper stud heads 8. The two edgesof the flanges 10 of the spacing rail 5 each enclose the opposite edges8a of the stud head 8. Thus the stud head 8 is mechanically and tightlyclamped to the spacing rail 5.

In FIG. 3 it is shown that stud shaft 7 can, unlike the FIG. 2 version,also be produced with a smooth surface.

In an alternate version shown in FIGS. 5 and 6, projections 11 areprovided on the base of the rail 9 which engage in a central recess 12in the stud head 8, as shown in the cross section of FIG. 6. Theprojections 11 can be made by a center hole punch on the outside of thebase of the rail 9 and serve as a tightly fitting connection between thestuds 6 and the spacing rail 5.

Unlike the above, the version in FIGS. 7 and 8 provides a lip 13 whichis punched out of the base 9 of the spacing rail and bent. The lips 13are for positioning of the stud heads 8. In FIGS. 7 and 8 the flanges 10are shown in an intermediate stage of the production. The flanges 10 arebent through an angle for insertion of the stud heads 8. Afterpositioning of the stud heads 8 at the lips 13 the flanges 10 are foldedto fasten the stud heads 8 in the aforementioned manner. It is alsopossible to fold the flanges 10 in a manner to allow the possibility oflater shifting the position of the studs 6. The movement could belimited by the lips 13 or in any other manner. Thus an adjustment of thestudrail is possible.

FIG. 9 it is shown that openings 14 may be provided in the base 9 of thespacing rail 5 which improve the connection between the surroundingconcrete and the spacing rail 5.

In FIG. 10 a rectangular opening 15 is presented which is cut out of thebase of the spacing rail 9. A chair 16 can be inserted and held inposition in this opening to maintain the minimum distance between thebase of the spacing rail and the concrete formwork. If the length of theopening 15 is larger than the width of the chair 16 it is possible toadjust the position of the studrail relative to the chair 16 which isfastened to the formwork.

If the spacing rail 5 is fabricated from stainless steel, its distanceto the concrete surface can be reduced to less than the minimum concretecover required for steel susceptible to corrosion.

The cross-section of the spacing rail 50 shown in FIG. 11 is mainlyU-shaped and also formed out of a single strip of sheet metal.

FIG. 11 shows the spacing rail 50 prior to inserting the studs 6.

Unlike the previously described example of the spacing rail where thebase of the rail 9 is flat, the base of the spacing rail 52 illustratedin FIG. 11 has an inwardly convex curvature of a specified radius Rprior to inserting the stud 6. On both sides of the base 52, the flanges54 develop into an S-shaped cross section beginning at an inwardlyconcave clamping section 56 connected to the base 52. The two clampingsections 56 enclose the edges of the stud head 8 when assembled.

Above the clamping sections 56 there is an inwardly cambered section 62which is adjacent to the edge strip 58. The two edge strips 58 of thespacing rail 50 diverge to the outside to facilitate the insertion ofthe stud heads 8 whereby the two edges of the flanges 54 act as a springand can be bent outward. The stud head 8 is clamped by the springyspacing rail 50 as shown in FIGS. 12 and 13.

The uppermost edges 60 of the edge strip 58 of each flange 54 are spaceda distance B apart whereas the opening width A of the U-shaped spacingrail 50 is defined by the distance between the inwardly camberedsections 62. The height of the spacing channel is given as C. For afavorable configuration of a spacing rail 50 the following dimensionswere selected:

a) the height C of the trough 50 is approximately 1.1 D where D is thediameter of the stud stem 7;

b) the radius of curvature of the rail base 52 is approximately 1.5 Ewhere E is the diameter of the inserted stud head 8;

c) the distance between the profile edges 60 is approximately 0.95 E;and

d) the opening width A between the inwardly cambered sections 62 isapproximately 0.75 E before inserting the stud.

As shown in FIG. 13, the stud head 8 is flat 8b on two opposite edgeswhich are aligned in the spacing trough 50. When inserting the stud 6the head of the stud 8 has to be pressed against the flanges 54 to bendthem outward so that the stud head 8 can be pressed through the inwardlycambered sections 62 to be positioned as shown in FIG. 12. The outwardbent uppermost surface of the flange 58 serves as a lever to simplifythe widening of the space between the sidewalls 54. When the stud headis mounted in the spacing rail 50 the face of the stud head is pressedto the cambered base of the rail 52 thus flattening the cambered base52. The flanges 54 act like a spring. pressing the stud head 8 againstthe inwardly cambered sections 62 and holding it in the spacing rail 50.

In this form the spacing rail 50 also ensures that the position of thestuds 6 is maintained in the reinforced concrete slab, in particular thepreset spacing of the studs.

In the example shown in FIGS. 11-13, the cross sections of the spacingrail 50 and the flexural rigidity of the spacing rail ensure that theconcrete is confined behind the anchor head 8. The concrete behind theanchor head 8 is confined between the outward edges of the flanges 58and the cone shape of the anchor head 8. This increases the compressivestrength of the concrete and allows the use of smaller stud heads 8 thanwithout the aforementioned detail. Finally, the spacing rail 50 alsodistributes the anchorage forces to an area larger than the stud head 8itself The flexural rigidity of the U-shaped spacing rail 50 enables thetransfer of the anchorage forces along a portion of the spacing rail 50.This also allows to choose a relatively small diameter for the stud head8.

In FIG. 14 it is shown that both heads 8 of a stud 6 can be attached toa spacing rail 50 or 64, respectively. It is also possible to attach thestud head 8 at the opposite end of spacing rail 50 to a correspondinglyshaped rail segment 65.

A second continuous spacing rail 64 can also be used if this rail doesnot interfere with the placement of further reinforcing elements. Ifthere are other reinforcing elements placed perpendicular to the spacingrail, as for example in a reinforced concrete slab, rail segments 65 canbe used. The gap 66 simplifies the placement of further reinforcingelements. To achieve larger gaps 66 the rail section 65 can be turnedthrough 90° as shown on the left hand side of FIG. 14.

FIG. 15 shows a greatly simplified schematic of a production of thestudrails 1 shown and described in FIG. 1, 2 and 4. A strip of sheetmetal 18 is unreeled from a sheet metal coil 17. In a punch press 19holes 14 and/or spacer openings 15 are punched out as shown in FIGS. 9and 10.

In a roll-forming machine 20 following the sheet metal strip 18 theflanges of the strip are rolled upwards. In the rail formed in this wayone stud head 8 is inserted from a stud magazine 6. The flanges 10 ofthe sheet metal strip 18 are folded afterwards to fasten the stud heads8. This may be achieved by using rollers 21. Afterwards the railsegments 18 with mounted studs 6 are cut to the desired length using acutter 22. The cutter 22 can also be placed before the stud 6 areinserted, as shown in FIG. 15 with a dashed-dotted line.

While the edges of the sheet metal band 18 are formed upwards by using arolling process as described in the design example, this can also bedone by bending the edges of the sheet metal strip in a bending machine.Instead of folding the edges of the sheet metal strip 18 to fasten thestuds 6 in a rolling process as described above, the edges of the sheetmetal strip 18 can also be folded in a bending process.

We claim:
 1. A studrail for shear reinforcement of a reinforced concretemember comprises a spacing rail (5, 50) and a pluraity of studs (6)arranged parallel to each other and secured at one end to the spacingrail (5, 50), each of said studs consisting of an elongate shaft (7)which is provided at both ends with an enlarged dish-shaped anchor head(8), said spacing rail (5, 50) consisting of a sheet metal rail having aweb (9, 52) which contacts a front end of the anchor heads (8) and whichholds the two opposite edges (8a) of each anchor head (8) with twofolded edges (10, 54) of the spacing rail (10, 54) wherein inner face ofthe web (9) is provided with projecting stops (11, 13) arranged at equalinterval in the longitudinal direction of the rail.
 2. Studrailaccording to claim 1, in which the edges of the spacing rail (10, 54)clamp the edges of the anchor heads (8a).
 3. Studrail according to claim1, in which the anchor heads (8) can be moved over a limited lengthalong the spacing rail (5).
 4. Studrail according to claim 1, in whichthe stops are punched out of the web (9) of the spacing rail formingmetal lips (13).
 5. Studrail according to claim 1, in which the stopsare lugs (11) projecting from the surface of the web (9) and fittinginto a central depression (12) in the anchor head (8).
 6. Studrailaccording to claim 1, in which the web (9) is provided with perforations(14).
 7. Studrail according to claim 1, including a plurality of chairs(16) and openings (15) provided in the plane of the web (9) for theinstallation of said chairs (16).
 8. Studrail according to claim 7, inwhich the chairs (16) can be moved in the opening (15) in the directionof the longitudinal axis of the studrail.
 9. Studrail according to claim1, in which the two flanges (54) of the spacing rail (50) are providedwith an outward curvature towards the flange edge (58).
 10. Studrailaccording to claim 9, in which the flanges are S-shaped in crosssection, producing an outward bent clamping segment (56) for each anchorhead (8) adjacent to the web face (52) of the section as well as aninward bent segment (62) adjacent to the flange edge (58).
 11. Studrailaccording to claims 1, in which the web (52) is convex towards theinside face of the web.
 12. Studrail according to claim 1, in which bothanchor heads of a stud (6) are connected with a spacing rail (50 or 64)or with an appropriately shaped rail segment (65).
 13. Process tomanufacture a studrail according to claim 1 characterized by thefollowing manufacturing steps:a) a metal strip is pulled from a coil ofmetal strips; b) the edges of the metal strip are bent up and projectingstops are formed on the inner face of the web,; c) in the metal stripthus formed the studs are inserted at one of the anchor heads,; d) thebent-up flanges of the molded metal strip are bent over to clamp theanchor heads.
 14. Process according to claim 13, in which segmentsprovided with studs are cut from the formed metal strip.
 15. Processaccording to claim 13, in which the flanges of the metal strip are bentup by a rolling process.
 16. Process according to claim 13, in which theflanges of the metal strip are produced by a bending process. 17.Process according to claim 13, in which the flanges of the metal stripare folded over by a rolling process.
 18. Process according to claim 13,in which the flanges of the metal strip are folded over by a bendingprocess.
 19. Process according to claim 13 in which the metal strip isperforated.